John Curl's Blowtorch preamplifier part II

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That's Mr.Bessel to you Bob..............dropping names again?:D

Sorry, I couldn't resist.

Jam

It's also nonsense. There is a difference between name dropping as in 'I had lunch with Mr Bessel, therefore I am right' or invoking a mathematical process called a 'Bessel function' to explain something. I'm sure you get the not-so-subtle difference, Jam.

jd
 
Talk about 'name dropping'. In order to test a hunch, I asked Mitch Cotter, who had told me that he worked for the Fermi group in WW2, whether he had actually met and worked with Enrico Fremi, himself.
This is what he told me:
He and his other young associates were putting together a cyclotron, and had to align the magnetic assembly associated with it. Apparently, it takes some tweaking and adjustment to the magnetic fields to get it right. Well they were having problems, so they called in Enrico Fermi, himself.
He came, talked to everyone about the situation, then asked for someone to get him a dinner fork. Once, equipped with the fork, he went inside the cyclotron, felt around with the fork, and it was aligned in about 1 hour. How is that for a story.:worship:

Mitch also read what was here, this morning, and reminded me 'not to suffer fools, gladly' apparently a quote from Voltaire.
He also sent me some supporting material, but I can't make any sense of it, as applied to this specific situation. Would you like me to send it to you, Janneman? Perhaps you could post the relevant info from your website to this one, if you find something important.
 
Bob, I don't yet have the background to fully give you any real input on your questions. However if you look on p. 15-26 of the reference book: "Electronics Engineer's Reference Book' 4th edition, by L.W. Turner, you will see the added distortion pattern that is superimposed on the standard IM byproducts. Many other reference textbooks will give a similar pattern, when showing FM generation. The extra terms are composed of Fp-Fm and Fp+Fm as an example. I hope this helps.
 
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[snip]He also sent me some supporting material, but I can't make any sense of it, as applied to this specific situation. Would you like me to send it to you, Janneman? Perhaps you could post the relevant info from your website to this one, if you find something important.

Absolutely. Any documentation related to this I will gladly host.

jd
 
Bob, I don't yet have the background to fully give you any real input on your questions. However if you look on p. 15-26 of the reference book: "Electronics Engineer's Reference Book' 4th edition, by L.W. Turner, you will see the added distortion pattern that is superimposed on the standard IM byproducts. Many other reference textbooks will give a similar pattern, when showing FM generation. The extra terms are composed of Fp-Fm and Fp+Fm as an example. I hope this helps.

Exactly so, Fp+/-(2*k+/-1)*Fm where k is an integer, also related to the order of the Bessel functions, this is what everybody around is telling you.

So, how is this making the FM spectral components "harmonicly unrelated" and how large should be the FM modulation so that the +/- sidebands are significantly apart from Fp?
 
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[snip] Would you like me to send it to you, Janneman? Perhaps you could post the relevant info from your website to this one, if you find something important.

John, it is small enough to directly post it here for all to download etc. Since this appears to be from Wikipedia, it can probably be downloaded from there as well.

jd
 

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Well, they are sitting right there on the Graph that is fig. 3. Why don't you tell me, if you will just look at the graph.
I has emulated the FM modulation by FM modulating a 5KHz test tone with a 700 Hz modulation frequency and just playing with the modulation level. You can too!
 
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Well, they are sitting right there on the Graph that is fig. 3. Why don't you tell me, if you will just look at the graph.
I has emulated the FM modulation by FM modulating a 5KHz test tone with a 700 Hz modulation frequency and just playing with the modulation level. You can too!

Not sure who you address or what graph, but reading the posted piece it looks like inharmonic components are created with an inharmonic modulation frequency. How does that relate to the audio amp case discussed, I'm not sure, I'm skating on logic here, not on knowledge, I admit.

Anyway, inharmonic distortion does apparently occur in mechanical systems:

"Subharmonic and Nonharmonic Distortions Generated by High-Frequency Compression Drivers
Acoustical and electrical measurements are made of several commercial high frequency compression drivers with sine wave inputs at various power levels. The results show outputs containing not only the typical levels of upper harmonics, but also subharmonics and nonharmonically related content. These other distortion products are caused by certain modes of vibration of the domed diaphragm assembly. A review of parameter selections for the moving system of a compression driver is given.

Author: Hubbard, Jerry K.
Affiliation: Altec Lansing Corporation, Oklahoma City, OK
AES Conference:6th International Conference: Sound Reinforcement (May 1988)
Paper Number:6-029 "

jd
 
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Hi John,
What I can tell you about FM modulation is from direct experience. A single frequency modulation of a carrier is identical as a single frequency of phase modulation. The HP product manual for the RF generators I have state this clearly. Indeed, if I phase modulate a carrier with 1 KHz and demodulate it using an HP 8901A (modulation analyzer), I get the same result as when I take another HP RF generator and FM modulate the carrier with a 1KHz tone. They also look the same on my spectrum analyzer or oscilloscope as well. So in this case, theory and practice align nicely. I haven't really bothered to try and decipher what happens if you phase modulate a carrier with a complex, multi-frequency signal, but the manuals indicate that phase and frequency modulation differ in those cases.

I figured I would at least report what I have read on this, and also what my direct observations were.

John, I do learn from you when you speak directly and point to the supporting information that is freely available and easy to get at. Beyond that, if you want to make a point, it really is your job to support what you say. If you are going to refer to what another person has said, then direct us to a paper or post that person has made. There is a reason why "hear-say" evidence is not normally admissible in a court of law. A small change in wording can completely change the meaning of a statement. This is why it's dangerous for people to accept what you say without the source. In fact, you don't always completely understand the issue. That's okay and natural, but you must allow that you may be mistaken some times. This is where things break down when you are pushing a point. No evidence that can be confirmed isn't really worth a great deal.

To your other point, yes I am a moderator. However I am also a member. I can and will speak my mind where I see a need. This is exactly what I am doing, like it or not. I think that I've been pretty clear by now on what you do that bothers me. I've stated this again in this post earlier on. Treat people around you with more respect, they do not deserve any less.

-Chris
 
Not sure who you address or what graph, but reading the posted piece it looks like inharmonic components are created with an inharmonic modulation frequency. How does that relate to the audio amp case discussed, I'm not sure, I'm skating on logic here, not on knowledge, I admit.

Anyway, inharmonic distortion does apparently occur in mechanical systems:

jd

If you "ping" a 10MHz crystal with a square wave you will get some 10MHz out. An amplifier with significant resonant energy storage i.e. class D might be made to make all kinds off stuff. I don't think that is an issue here, and certainly not in the uA741 (I assume a PIM baddie).
 
Chris, I am doing everyone interested, a GREAT BIG FAVOR just bringing up these new 'breakthroughs' (at least for us) in audio design. I don't have to prove this stuff in a court of law. Who cares? I also don't have the time, energy, or patience to write a technical paper about it, these days, and have it published, if possible, after going through the referee process, composed of guys like Bob Cordell or Scott Wurcer. Why would I bother? Although I have written articles for journals and magazines, in the long past, 30 years ago, when I thought it important to do so. It just isn't worth it, today.
Everyone, take it, disprove it, or leave it. It is your gain or loss, not mine.
Except, Nelson, Charles, and I aren't even considered design engineers by you, even though Humphrey Ins put 'Sr Design Engineer' on my business card, 25 years ago.
However, I prefer 'Vice President of Engineering' the title on my business card with LINEAGE INC. more than 20 years ago. :cool:
 
I was always taught that narrowband fm is essentially like am but with the phase of the sidebands just different. I completely understand that this is not the case for high-deviation fm, where Bessel functions are essential to a proper understanding (but I do not believe that PIM falls in the category of high-deviation fm).

You are right here absolutely, about phase of sidebands: yesterday I've posted the link on an article that deals with "How to tell, is it AM or FM"? It seems to me, nobody paid attention.
The truth is, quadrature modulation was used in radio for FM modulation. I.e. the case of modulation of one sine wave by some signal. Products are harmonically related. But in case of phase inter modulation the result is a quite different garbage.
 
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So this is the Fig 3 John has brought up. What is that confounded 'blip'?

jd
 

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